Why do they need to measure Everest again?

Mountain measurement is not a precise art. Mountains are usually a long way from the sea, and measurements are made from sea level. Both keep shifting. In 1852, a British team put the height of Mount Everest - the world's highest peak - at 29,002ft and in 1856 at 29,028ft or 8,848m. In 1975, the Chinese had a closer look and came up with the same figure. In 1999, a US expedition used the global positioning satellites (GPS) system to pinpoint the highest peak at 29,035 ft or 8,850m.

Now, worried that global warming might be taking Everest down a peg or two, as the glaciers melt and the Himalayan snowline rises, the Chinese are to have another go. A Chinese Academy of Sciences team has announced that it will use radar and GPS to fix the peak to new levels of accuracy.

This is unlikely to settle the matter. That is because Mount Everest keeps moving. The Himalayas have been crumpling upwards ever since India began colliding with Asia about 60m years ago, and at the same time crumbling away as monsoon rains bucket down every year. The mountain keeps moving to the north-east, by several centimetres every year, once again under pressure from the tectonic conveyor belt that keeps earthquakes rumbling along the mountain faultline.

And finally, all mountains are subject to isostatic forces: they begin to subside almost as soon as they begin to build, because the rocks in the mantle far below them ooze away to a kind of gravitational equilibrium. So Everest is rising, eroding, shifting and sinking. And now, if the Chinese are right, it is also melting. They believe it may have lost 1.3m as a result of global warming.